Fluidic ac amplifiers

ABSTRACT

A TUNED FLUID AMPLIFIER CIRCUIT IS DISCLOSED WHEREIN ALTERNATING FLOW SIGNALS IN A FREQUENCY RANGE ABOUT A PREDETERMINED FREQUENCY ARE AMPLIFIED TO A SIGNIFICANTLY GREATER DEGREE THAN EITHER DIRECT FLOW SIGNALS OR ALTERNATING FLOW SIGNALS OUTSIDE SAID FREQUENCY RANGE. A LOW IMPEDANCE AMPLIFIER IS EMPLOYED UTILIZING CONTROL PORTS SITUATED CLOSE TO THE POWER STREAM IN ORDER THAT THE CONTROL FLUID PROVIDES A TRANSVERSE PRESSURE GRADIENT FOR SELECTIVELY DEFLECTING THE POWER STREAM RATHER THAN EMPLOYING MOMENTUM INTERCHANGE BETWEEN CONTROL AND POWER FLUID. THE RECEIVERS AND CONTROL PORTS ARE OF LARGE CROSS SECTION RELATIVE TO THE POWER NOZZLE TO MINIMIZE FLOW IMPEDANCE AND THEREBY OPTIMIZE THE CIRCUIT Q FACTOR. THE OUTPUT PASSAGES OF THE AMPLIFIER MAY COMRPISE RESONANT FLUID PASSAGES IN WHICH STANDING WAVES ARE PRODUCED AT THE PREDETERMINED RESONANT FREQUENCY AS ESTABLISHED BY THE RESONANT PASSAGE LENGTH, OR LUMPED-PARAMETER TUNED CIRCUITS MAY BE CONNECTED TO THE OUTPUT PASSAGES.

United States Patent [72] inventors Larry R. Moore;

Robert F. Turek, Silver Spring, Md. 2| AppLNo. 754,002

[22] Filed Aug. 20, 1968 [45] Patented June 28,1971

[73] Assignee Bowles Fluidics Corporation Silver Springs, Md.

1541 FLUlDlC AC AMPLIFIERS 24 Claims, 7 Drawing Figs.

[52] U.S.'Cl l37/81.5

[51] Int. Cl. Fl5c1/04 [50] Field of Search 137/815 [56] References Cited UNITED STATES PATENTS 3,457,935 7/1969 Kantola 137/81.5 3,486,520 12/1969 Hyereta1.... 137/815 3,223,101 12/1965 Bowles 137/815 3,228,410 l/1966 Warren et al. 137/81.5 3,233,522 2/1966 Stern 137/81.SX 3,238,958 3/1966 Warren et al. 137/81.5 3,327,725 6/1967 Hatch, .11. 137/815 3,362,421 1/1968 Schaffer 137/81.5

Primary Examiner-Samuel Scott Anomey Rose & Edell ABSTRACT: A tuned fluidic amplifier circuit is disclosed wherein alternating flow signals in a frequency range about a predetermined frequency are amplified to a significantly greater degree than either direct flow signals or alternating flow signals outside said frequency range. A low impedance amplifier is employed utilizing control ports situated close to the power stream in order that the control fluid provides a transverse pressure gradient for selectively deflecting the power stream rather than employing momentum interchange between control and power fluid. The receivers and control ports are of large cross section relative to the power nozzle to minimize flow impedance and thereby optimize the circuit 0 factor. The output passages of the amplifier may comprise resonant fluid passages in which standing waves are produced at the predetermined resonant frequency as established by the resonant passage length, or lumped-parameter tuned circuits 4 may be connected to the output passages.

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i1 nllllliillll PATENIEI] JUN28 I97! SHEET 1 OF 3 GAJN FLUIDIC AMPLIFIER FREQUENCY w I GAIN PIGyz TUNED FLUIDIC ACAMPLIFI E R FREQUENCY we FIG-3 UTILIZATION ELECTRONIC FLUIDIC SQQQ Ei BAND'PASS C C I HIGH F L ER I 5 CURRENT.(FLOW) AMPLIFIER I L W HIGH LOW L L NOTCH FILTER LOW LOW VOLTAGE (PRESSURE) L I f AMPLIFIER I W LOW G INVENTO RS LQRRY R. MOORE 6n ROBERT F. TUREK ATTORNEY PATENTEDJUN28I97| K 3587.604

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NIH"! Him 3 l V LARRY R. MOORE 6 ROBERT F. TUREK BY v /a mr ATTORNEYS v Q MINIMUM FLUIDIC AC AMPLIFIERS BACKGROUND OF THElNVENTlON The present invention relates to fluidic amplifiers and, more particularly to tuned fluidic amplifiers suitable for amplifying oscillatory fluid signals.

Prior art fluidic systems employing fluidic amplifiers of the proportional-typefsuch as that illustrated and described in U.S. Pat. No. 3,l22,l6 5, are limited in part by the following inherent limitations of the amplifiers themselves: drift; limited gain; noise; and relatively slow response time. The following is a brief description of these inherent problems:

I. Drift-Prior art utilization of proportional fluidic amplifiers, of the type in which a power stream of fluid is deflected by a control signal relative to one or more output passages requires establishment of a reference position for the power stream for zero input signal level from which deflections of the power stream are to be monitored by virtue of the fluid received of the output passages. Drift, or zero point shift, is the variation of the power stream v position relative to the established quiescent position for zero input level.- This phenomenon causes an output signal indicativeof the'presence of an input signal to occur when there is, in fact, no input signal present. in addition, when an input signal is received, the power stream is deflected to a position relative to the position to which it drifted rather than relative to the desired reference position. This drift phenomenon in a proportional fluidic amplifier produces undesirable inaccuracies which can be cumulative in a fluidic system. For example, consider a plurality of cascaded fluidic amplifiers of the proportional-type; if there is drift in each of the cascaded stages, the cumulative effect of the drift is manifested as a gross error at the output port of the last stage of the amplifier.

2. Noise-In fluidic amplifiers of the proportional type, internally generated noise signals are often inevitable, acting at times to limit the minimum information signal discernable by the amplifier. Much of the internally generated noise is in the form of sinusoidal signals occuring at discrete frequencies. The effect of this noise on the amplifier output signal is to produce noise frequency components in the amplified signal thereby distorting the signal.

3. Limited Gain-Variation of gain in proportional fluidic amplifiers is not usually a significant problem. However, individual amplifier gain is relatively low for many applications and therefore a large number of amplifier stages must be employed. Gain and noise are interlinked by the fact that low gain amplifiers require a large number of stages to reach a given gain and noise is normally a function of the number of amplifiers for low gain units. lt is therefore desirable to increase the individual amplifier gain so that the number of stages required to achieve a given gain and hence the noise produced in the system may be reduced.

. 4. Response Time-If the gain of fluidic amplifiers can be increased, then the number of amplifiers required to achieve a given gain can be reduced and therefore the signal path length through the amplifier circuit may be reduced. By reducing the signal path length in a given system, the response time of that system will automatically be improved;

Fluidic amplifiers having the disadvantages and limitations described above have been-utilized in the prior art as directflow" (DF) amplifiers; that is, the variable amplitude input signal to be amplified is applied directly to the control port of the amplifier to deflect the amplifier power stream from a reference position as a function of input signal amplitude. Direct-flow or DF fluidic amplifiers are analogous to DC electronic amplifiers in this sense. Electronics technology on the other hand has solved the problems and limitations described above by employing AC amplifiers. More particularly, the use LII of AC modulated-carrier systems in electronics has eliminated drift and minimized'noise by utilizing as the information signal the amplitude of an alternating or AC signal rather than a DC signal amplitude. Since,.in an alternating-flow or AF fluidic system, the quiescent operating condition for the amplifier would be an oscillatory mode about a reference position, the drift problem is substantially eliminated. In addition, electronic technology has employed tuned" AC amplifiers. to provide highly resonant response characteristics for the amplifier whereby the gain at the resonant frequency of the amplifier circuit is substantially higher than the gain of a counterpart DC amplifier and wherein the noise rejection capabilities of the amplifier are improved since the response of the amplifier outside of its limited frequency pass band is greatly attenuated. The tuned AF or alternating-flow approach to amplification of fluid signals is the primary concern of the present invention.

It is therefore an object of the present invention to provide a tuned fluidic alternating-flow modulated-carrier system.

it is another object of the present invention to provide fluidic amplifiers having a higher gain per stage, greater signal sensitivity, greater accuracy, and improved response time over prior art fluidic amplifiers.

ln employing AF or alternating-flow techniques to amplify DF or direct-flow signals, it is necessary to first employ modulation techniques to convert the DF signal amplitude to a variable parameter of an oscillatory fluid signal which can then be processed accordingly in the AF amplifier circuit. Similarly, after amplification of the AF signal, demodulation techniques must be employed to recover the amplified version of the DF input signal from the amplified oscillatory signal. Modulation and demodulation techniques are well known in the fluidics art. For example, amplitude-modulation of fluidic signals may be readily achieved by the techniques disclosed in U.S. Pat. No. 3,428,067. Frequency-modulation techniques suitable for utilization in alternating-flow modulated carriers systems are exemplified by pressure controlled oscillators which provide oscillatory fluid output signals having a frequency which is proportional to the amplitude of an input pressure signal. Examples of pressure controlled oscillators may be found in U.S. Pat. No. 3,238,960 and U.S. Pat. No. 3,348,562. Techniques for demodulating amplitude-modulated fluid signals may be found in the above-referenced U.S. Pat. No. 3,428,067 and in U.S. Pat. No. 3,292,648. in addition, techniques for demodulating frequency-modulated fluid signals may be found in U.S. Pat. No. 3,292,648.

Modulation and demodulation techniques being known, the remaining important element therefore in an alternating flow or AF modulated carrier fluid system is the AF amplifier with which the present invention is primarily concerned. More particularly, the required fluidic amplifier must be a high-gain narrow-band AF amplifier. It has been found that conventional direct-flow or DF amplifier elements, which are designed for maximum pressure gain, generally do not have appropriate impedance characteristics to provide high gain narrow-band alternating flow amplification. Without proper impedance matching and minimization of resistive losses, the amplifier pass-band becomes too wide, resulting in insignificant gain improvement over conventional direct-flow operation.

It is therefore an object of the present invention to provide a high-gain narrow-band alternating flow amplifier for use in fluidic modulated-carrier systems.

It is another object of the present invention to provide a tuned fluidic amplifier suitable for alternating-flow operation in which resistive losses are minimized and impedance matching is provided.

The advantages of a tuned AF amplifier over a conventional DF amplifier may be best understood by referring to FIGS. 1 and 2 which are respectively plots of the frequency response of a DP fluidic amplifier and a tuned DF fluidic amplifier v operable in the AF or alternating flow mode. Direct-flow amplifiers, as illustrated in H6. 1, have a frequency response in which signal amplitude becomes severely attenuated after some predetermined cutoff frequency represented as w, in FIG. I. For frequencies below w, the gain characteristic is substantially flat representing a substantially constant gain. The effect of tuning in a fluidic amplifier produces the characteristic shown in FIG. 2. It is noted that instead of falling off at some predetermined rate beyond the frequency the response characteristic peaks at a much higher gain level than the gain level in the substantially flat region of the characteristic. Of course, the resonant peak need not necessarily occur at frequencies above 0),, but rather may occur anywhere in the spectrum (within limits of the amplifier configuration) according to the resonant frequency desired for a given circuit.

Tuned amplifiers then may comprise DF amplifiers operating in an alternating flow mode and having appropriate passive tuned circuits connected either to their input ports, output ports or in a feedback loop between the output and input ports. The feedback concept suffers from the necessity of a very stable circuit, the higher the gain the greater the tendency of the circuit to become unstable; therefore, an adequate stability margin must be used in high gain tuned feedback amplifiers to prevent the circuit from being too sensitive to gain changes arising from variations in supply pressure or temperature. Even with sufficient margin to prevent instability, variations in the closed loop gain and resulting shift in the resonant frequency may be objectionable. These considerations do not rule out feedback techniques for developing tuned AF fluidic amplifiers, but they do suggest that a notable advantage, namely that of stability, may be achieved by utilized interstage tuning.

Tuning may be accomplished by using either the lumped parameter approach (fluidic inductor-capacitor circuits) or the distributed parameter approach (resonant fluid passage lines). In considering the utilization of fluidic inductor-capacitor circuits, FIG. 3 is provided to illustrate the passive circuits suitable for fluidic amplifier tuning. More specifically, FIG. 3 illustrates the various combinations of fluidic capacitors and inductors with their electrical schematic counterparts, the relative source and load impedances of each, and the primary utilization of each. The effectiveness of each of these circuits depends on their ability to detect signals without modifying them. A resonant circuit always includes two energy storage means; at resonance, energy is rapidly exchanged back and forth from one form to another. As a result, a signal applied to the resonant circuit at the resonant frequency is reenforced, while other frequency components are attenuated. This process is hindered if there is resistance in the interconnecting pathway or if there is an alternate path provided for the signal. While significant gain is possible, the amplified signal must be detected without affecting the resonance energy exchange. An amplified pressure signal should be detected by a high impedance device because the load provides an alternate path through which energy is dissipated. Flow amplification by a parallel resonance circuit on the other hand, should be detected by a low impedance device. In electronics, low impedances of various types are not difficult to provide; in fluidics, however, obtaining desired impedance relationships can be quite difficult.

Other important considerations with regard to amplifier tuning are the source characteristics. The parallel tuned circuit must be driven with a flow source. This is a high impedance source relative to the load so that the load variations do not affect the fluid flow significantly. The series resonant circuit, on the other hand, must be driven by a pressure source having a minimum impedance.

It is possible to exchange the fluidic inductors and capacitors in the circuits of FIG. 3 to obtain othervariations in circuit performance. However. all fluidic capacitors act as though they were connected in parallel with the circuit to which they are connected, series-type capacitors being nonrealizable at the present time in fluidics.

In electronic circuits, capacitors usually are considered to have negligible inductance. inductors are considered to exhibit negligible capacitance, and electrical connecting wires exhibit negligible reactance. In fluidics the lumped parameter technique implies a capacitor having a large volume compared to inductors or transmission lines, and at the same time, capacitors and transmission lines must have a small inductive reactance in comparison to that of the inductor. These qualifications are reflected in the proportions of the schematically illustrated elements in FIG. 3.

When considering the various circuits of FIG. 3 as resonators, it is important that the wavelength of the signal be large compared tb the size of the resonator. The fluidic capacitor is assumed to be lossless; however, significant resistance does exist in the inductor. The resistance in the inductor can have a significant effect when one tries to attain a high-gain narrowband amplifier using a tuned circuit. More particularly, the quality factor O, which provides an indication of the gain and bandwidth in a tuned circuit (the greater the value of Q, the higher the gain and narrower the bandwidth) may be expressed as follows in an L-C circuit with lossless capacitors but with resistance in the inductor:

where (0,, equals resonant frequency, R equals inductor resistance, and L equals the inductor inductance. The inductor resistance R on the other hand may be shown to be equal to where AP equals the pressure drop across the inductor, m equals the flow rate through the inductor, v equals the fluid viscosity, I equals the inductor length, A equals the inductor area, and g equals the gravitational constant. Similarly, it may be shown that the fluid inductance L can be written as:

It is interesting to note that the length of the inductor does not effect Q. Rather, in order to minimize the resistance of the inductor and hence maximize the value of Q, the cross-sectional area A of the inductor should be made as large as possible. Simple connections between inductors and capacitors such as those shown in FIG. 3 are generally not desirable in highly tuned narrow band circuits where sustained resonance is desired. More particularly, since flow exists between the two energy-stored elements, it is desired to minimize the DF or direct-flow impedance between the two elements and thereby reduce pressure losses of the flow alternating therebetween. Thus a sharp transition between capacitor and inductor is highly undesirable. The more gradual the transition between capacitor and inductor becomes, the more efficient the tuned circuit becomes and the greater the value of Q. Eventually, the graduation of transition between the inductor and the capacitor can be carried to an extreme until the identities of the inductor and capacitor are lost, in which case, empirical methods would be required to establish resonant frequencies; however, the efficiency of the circuit would be increased.

The series LC circuit illustrated in FIG. 3 (the bottom circuit) produces pressure amplification. The pressure in the capacitor must be sensed by a high impedance device. Therefore, the amplifier control port to which the output of this series LC circuit is to be connected must be small compared to the receiver port of the amplifier driving the circuit. A stability problem is encountered if the source amplifier is much larger than the load amplifier. Moststream interaction amplifiers become stable if the load is too small (small flow, high impedance). However, appropriate vents for the receivers can be added to reduce the amplifiers sensitivity to load changes.

The parallel passive fluidic circuit illustrated in the second level of FIG. 3 amplifies the signal flow but offers no pressure gain. An appropriate source is a small amplifier, that is, an amplifier with narrow receiver passages and, because it drives a low impedance circuit, it should be stable. An amplifier with large control ports must be used to sense the flow signal through the inductor. It is seen therefore that the choice of a series or parallel LC tuned circuit depends upon the desire for pressure or flow gain. Pressure amplifiers are fluidic elements in which the primary signal parameter to be amplified is pressure even though a certain amount of flow gain may be achieved in the process. Flow amplifiers are primarily concerned with flow amplification even though pressure amplification may also be achieved. Most work in fluidics at the present time is done with pressure amplifiers, primarily because the load is most often a high impedance device. It should be pointed out, however, that fluidic amplifierscan be designed to accept a flow-type signal and deliver a pressuretype signal, or vice versa, therefore acting as pressure-to-flow or flow-to-pressure converters as the case may be. The conversion of a flow signal to a pressure signal could possible be accomplished in a demodulating amplifier. Therefore, the possibility of utilizing flow-type amplifiers as opposed to pressure amplifiers should not be dismissed. It is interesting to note that relative to the power nozzle size, the flow amplifiers have larger receivers than the pressure amplifier and for this reason have less resistive loss and higher flow efficiency. This is of primary importance in highly tuned circuits which are detrimentally affected by resistive losses.

in addition to utilizing tuned passive circuits comprising lumped parameter elements of the type described above, resonant lines may also-be used for interstage tuning whereby to provide a distributed parameter tuning technique. Resonant fluid flow passages develop standing waves in response to pressure disturbances at one end or the other thereof. As was the case in considering the lumped parameter approach to tuning, the resistive losses in resonant passagesmust be kept to a minimum in high-gain narrow-band amplifiers, and appropriate impedance terminations must be provided to maximally sustain the standing waves. It is difficult to separate the amplifier output passage and the resonant passages for purposes of analysis. The length of the resonant passage, of course, deten'nines the frequency of the standing waves developed therein. A straight tube for example closed at one end will resonate at odd multiples of its fundamental frequency. A straight tube open at both ends will resonate at all integer multiples of the fundamental frequency. A conical tube closed at the vertex will resonate at all integer multiples of its fundamental frequency, just as the open tube does. The taper thus produces an effect of making the closed end of the cone appear to be open. It is important therefore to note that the influence of tapers or size variations in resonant passages cannot be neglected and the amplifier receivers and control ports mustbe considered as a portion of the resonant passage when such passage is connected to receivers and/or control ports.

. It is important to note also that high impedance fluidic loads can be obtained only with abrupt reduction in line size. If the size reduction is produced through a tapered section, the al' ternating-flow impedance is transformed and would no longer appear high. This is, however, contrary to common prior art design practice in fluidicswhere only direct-flow is considered and this factor accounts for some of the difflculties encountered when one attempts to implement alternating-flow circuits using most conventional direct-flow type fluidic am- .plifiers.

Standing wavesin a pipe or tube do not necessarily provide flow or pressure'gain. if a tube has identical terminations and similar source and load impedances, resonance will occur with the load impedances matched. if the impedances are identical, no amplification will result. A one-quarter wavelength tube resultsif the impedances are very much different. Depending upon which impedance is high, this tube will provide flow gain or pressure gain as desired. A high impedance source with a low impedance load for instance will result primarily in flow gain. The impedance requirements are identical to those of the lumped parameter circuits.

Whichever method of tuning is employed, lumped or distributed parameter it is critical to good alternating-flow amplification that a good direct-flow amplifier be provided, capable of amplifying signals at the desired frequencies. The gain of most prior art jet-interaction type amplifiers falls off rapidly above 300 cycles per second. Generally, these amplifiers are designed for high direct-flow pressure gain, with little consideration being given to the impedance requirements imposed by acoustic signals of relatively short wavelengths. Control ports for example in conventional direct-flow amplifiers, are terminated abruptly creating a poor impedance match with the interaction region. in addition, tapered control ports and receivers may have adverse effects on circuit performance. it is important therefore that a fluidic amplifier of suitable frequency response be provided in order for alternating-flow systems to be realizable in fluidics.

it is therefore an object of the present invention to provide a tuned fluidic amplifier of the stream-deflection type which is suitable for alternating-flow amplification.

It is another object of the present invention to provide an alternating-flow amplifier to be utilized with tuned passive fluidic circuitry for providing alternating flow amplification with gains substantially higher than direct flow gains currently achievable with fluidic amplifiers.

There are two primary methods currently available by which a power stream in a proportional direct-flow fluidic amplifier can be deflected by transversely directed control fluid.

The first uses the momentum of a control stream to effect deflection, and may be exemplified by the fluidic amplifiers illustrated and described in US. Pat. No. 3,122,165. The second method for effecting power stream deflection in direct-flow proportional amplifiers is described and illustrated in an article by F. T. Brown and A. K. Simpson entitled Research in Pressure Controlled Jet Amplifiers, published by the Clearing House for Federal Scientific and Technical Information, A.D. 605860, 1963. The Brown and Simpson method provides a pressure gradient at the control ports across the power stream, the control port and power stream being very closely coupled thereby reducing the need to transmit signals across a portion of the amplifier interaction region.

- Brown and Simpson set forth different geometrical relationships for optimum pressure, flow and power type fluidic amplifiers. The optimum geometry for a flow amplifier which has minimal resistive losses and is therefore of interest in providing tuned alternating-flow amplifier elements, is described as comprising large control ports and receivers relative to the power nozzle. The efficiency of the Brown and Simpson flow amplifier is substantially greater than that of the pressure amplifier, a factor which favors the use of flow amplifiers and parallel passive circuits for tuned fluidic amplifiers.

SUMMARY OF THE INVENTION In accordance with the primary embodiment of the present invention, a tuned fluidic amplifier circuit is provided in which a low impedance amplifier is tuned by connecting resonant fluid passage lines to the amplifier output passages. Output passage widths at least as wide as the power nozzle and preferably three times the power nozzle width, are provided to minimize resistive losses in the amplifier and provide efficient flow transfer from the power nozzle to the receiver and tuned resonant output passage. The receiver or outputpassage itself forms part of the resonant fluid passage whose overall length determines the frequency of standing waves developed therein and hence the-resonant frequency of the tuned amplifier circuit. The amplifier control port terminates relatively closeto the power stream so as to minimize the distance through which the alternating flow input signals applied thereto must travel across the interaction region of the amplifier. Preferably the control port terminates at a distance approximately equal to one power nozzle width from the center of the power stream. The control port also is wide relative to the power nozzle, preferably three times the power nozzle width. Alternating-flow amplifiers of this type may be connected in cascade to provide a multistage, alternating-flow amplifier.

Alternatively, a low impedance amplifier may have a lumped-parameter resonant circuit connected to its input or output passage to provide the requisite tuning. The tuned amplifiers of the present invention may be used in a system wherein a variable amplitude signal is converted by either amplitude or frequency modulation to an oscillatory signal having a frequency which is limited to the pass band of the tuned amplifier. The oscillator signal is amplified and converted via a suitable demodulator to an amplified version of the variableamplitude input signal.

BRIEF DESCRIPTION OF THE DRAWINGS The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of several embodiments thereof, especially when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a plot of the frequency response characteristic of a conventional direct-flowfluidic amplifier;

FIG. 2 is a plot of a frequency response characteristic of a tuned fluidic amplifier;

FIG. 3 is a chart of passive tuned circuits suitable for use in providing tuned alternating flow amplifiers;

FIG. 4 is a plan view of a tuned alternating-flow amplifier according to the principles of the present invention;

FIG. 5 is a schematic illustration of a three stage tuned amplifier circuit employing lumped parameter interstage tuning; and

FIGS. 6 and 7 are schematic illustrations of fluidic modulated-carrier systems employing the .tuned alternating-flow amplifier of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 4 of the accompanying drawings, there is illustrated a tuned fluidic amplifier circuit designated generally by the reference numeral 10. Circuit 10 includes a fluidic amplifier having various cavities, passages and nozzles formed in a flat plate which is covered by a flat plate 12, the two plates being sealed in fluidtight sandwich relationship, one to the other, by conventional means. For purposes of clarity, the plates 11 and 12 are illustrated as being composed of clear plastic material. However, it should be understood that any material compatible with the working fluid may be utilized in the construction of the amplifier.

The amplifier includes a power nozzle 13 responsive to application of pressurized fluid thereto for issuing a power stream offluid into an interaction region 15. A pair ofsubstantially opposed control ports 17 and I9 communicate with the interaction region on opposite sides of power nozzle 13. A vent passage 21 communicates with interaction region 15 between power nozzle 13 and control port 17, and a vent passage 23 communicates with interaction region 15 between power nozzle 13 and control port 19. A pair of knife-edge configured sidewalls 25 and 27 define the downstream side of control ports I7 and 19, respectively, the apex or point of the knife-edge defining the downstream portion of the mouth of a respective control port. The walls 25 and 27 diverge from one another in a downstream direction.

A pair of output passages 29 and 31 communicate with the downstream end of interaction region 15, passages 29 and 31 being separated by a flow divider 33 having an apex in substantial alignment with the power nozzle-l3. The portion of interaction region 15 between the knife-edge sidewalls and the output passages has recessed sidewalls 35 and 37, respectively, which terminate in respective vent passages 39 and 41.

Vent passages 39 and 41 communicate with ambient pressure through respective vent ports 43 and 45 formed in plate 11. The purposes of vent passages 39, 41 is to minimize boundary layer effects between the power stream and the sidewalls of the-interaction region 15.

Output passages 29 and 31 are connected to respective fluid passages 47 and 49. Output passage 29 together with fluid passage 47 comprises a resonant output passage in which standing waves are developed in response to pressure disturbances appearing at the ingress orifice of output passage 29. Similarly, output passage 31 and fluid passage 49 comprise a resonant passage in which standing waves are developed in response to pressure disturbances appearing at the ingress orifice of output passage 31. The frequency of the standing waves in each of the resonant fluid passages is determined by the length of these passages, the length of both passages being equal for the amplifier of circuit 10. The downstream ends of fluid passages 47 and 49 are terminated in respective inlet ports of a load device 51. Load device 51 may be a further fluid amplifier or some fluid-operated utilization device, depending upon the circuit application.

The amplifier in circuit 10 is not a stream interaction type amplifier such as that disclosed in the various embodiments of U.S. Pat. No. 3,122,165. Rather, the deflection of the power stream issued from power nozzle 13 is achieved by the method described in the above-referenced article by Brown and Simpson; namely, by establishing a pressure gradient across the power stream by means of pressurized control fluid supplied to control ports 17 and 19. To this end, the control ports 17 and 19 are wide relative to the width of the power nozzle 13 and are terminated relatively close thereto, the requisite dimensions being discussed in detail hereinbelow. The effect of the control port configuration and the knife-edge wall configuration on the power stream are described in detail in the above-referenced article by Brown and Simpson. It is sufficient to state here that the control port configuration shown in FIG. 4 permits predictable effects on power stream deflection by selective application of a pressure gradient to control ports 17 and 19.

As described above, it has been found that flow-type amplifiers, as opposed to pressure amplifiers, are more efficient and better suited for narrow-band tuned amplifier circuits because of the lower resistive losses in flow amplifiers which permit attainment of much higher circuit 0 factors. The above-referenced publication by Brown and Simpson, at pages 118 through 123, provides a detailed analysis of the specific 'geometry required for provision of a flow amplifier. We have found that a flow amplifier of minimal resistance and sufficient for use in a tuned amplifier circuit is provided where the various orifices, ports and nozzles in FIG. 4 have the relative dimensions indicated in Table I.

Table I power nozzle width-W control port width3W output passage width-3W knife-edge spacing-2W Fairly good results insofar as tuning is concerned have been achieved in amplifiers having output passage widths as small as W and with knife-edge separations varying by as much as 20 percent from 2W. The resonant peak in the frequency response characteristic (see FIG. 2) of such amplifiers is somewhat wider and has a lower peak level than amplifiers having a receiver width of SW and a knife-edge separation of 2W. Control ports narrower than 3W are also feasible, the narrower the control port the greater the resistive loss for the output signal and the lower the resonance peak in the amplifier frequency response. It is important to note, however, that for some applications a relatively narrow band high gain response is not necessarily required but rather may be somewhat undesirable in view of the application to which the tuned circuit may be put. This will be better understood in view of the difference applications of the tuned circuit of FIG. 4 described below in reference to FIGS. 6 and 7.

The distance between the power nozzle and the apex of divider 33 in the amplifier of FIG.-4 is on the order of 8W-- 1 S W, variations of this dimension within this range having relatively minimal effects on the frequency response of the amplifier.

It is important whenattempting to maximize the gain and narrow the bandwidth of the frequency response of amplifier circuit 10 that the resonant output passage, including both output passage 29 and flow passage 47 for example, be of substantially constant cross section since variations in the passage width produce concomitant variations in flow impedance which significantly affect the Q factor ofthe tuned circuit. Naturally, where a broader-band lower-gain response is desired intentional variations may be provided in the cross section of the resonant passage, such as by providing a transition in passage width at the junction point between output passage 29 and flow passage 47 or by narrowing the downstream end of flow passage 47 to simulate a relatively high impedance orifice load or by otherwise varying the passage width.

Illustration of the resonant fluid passage as being connected to the amplifier output passage is not to be construed as limiting the scope of the present invention. More particularly, resonant passages may be connected to the control ports whereby to provide a resonant pass-band for input signals applied to the amplifier. The length of such resonant passages determines the resonant frequency of the circuit. Variations in passage size produce a lowering and broadening of the resonant peak in the circuit frequency response. of course, where a plurality of tuned amplifier stages are connected in cascade, the resonant lines interconnecting the output passage of preceding stages with the control ports of succeeding stages can be viewed as being connected to either or both the control ports and/or the output passages.

In addition, it has been found that the resonant passages can be curved relatively sharply without significantly affecting the frequency response characteristic of the amplifier circuit. This is advantageous in permitting amplifier circuit 10 to be formed in an integrated circuit plate of reasonably small dimensions in spite of relatively long resonant passages that may be required to produce low resonant frequencies.

It is to be understood, of course, that a number of stages of tuned amplifiers may be connected in cascade depending upon the gain desired in a particular circuit application. For an amplifier circuit having the relative dimensions described above in Table [,gains as high as 30 db. per stage at the resonant frequency peaks have been achieved. Naturally, if more gain-is desired, more stages may be employed.

Similarly, stagger tuning techniques may be employed in a manner analogous to stagger tuning techniques employed in electronics where it is desired to provide a broad-band highgain tuned amplifier; that is, a high gain over a broader frequency hand than the high gain band of a single amplifier stage. Thus, by tuning the various cascaded stages to slightly different frequencies, a relatively high-gain, broad-band frequency response may be achieved, having a flatter peak and sharper rate of cutoff than is achieved by detuning an individual amplifier stage. To achieve the tuning at different frequencies, one need only provide appropriate lengths for the resonant output passages of each amplifier stage. The output lines can be considered open ended if the load impedance, for example, the impedance ofload 51, is relatively low and therefore the resonance frequencies can be calculated in a relationship:f,.=u/)\ where f, is the resonant frequency, A is twice the length of the output line, and u is the speed of sound in air,

- generally assumed to be 1,100 feet per second but variable in accordance with differing temperature and pressure conditions. By varying the length of the resonant output passages,

In addition to the distributed parameter tuning technique employed for amplifier circuit 10, a lumped parameter tuning technique may be employed utilizing one or combinations of the passive tuned circuits illustrated in FIG. 3. An example of a lumped parameter tuned circuit is illustrated in FIG. 5 wherein three fluidic amplifiers 53, 55 and 57 are connected in cascade. The three amplifiers 53, 55 and 57 are of the low input impedance-type, for example, of the type illustrated in FIG. 4, to minimize resistive losses so that a narrow band high gain circuit may be achieved. As illustrated diagrammatically, the amplifiers are of increasing size from the first to the last stage so that each succeeding stage presents a relatively low impedance to the amplified flow from its preceding stage. The relative sizes of the power nozzle, output passage and control port may, if desired, be the same in any one stage as in any other stage, but the absolute dimensions of these nozzles, passages and ports increase in succeeding stages.

Amplifier 53 includes a power nozzle 59 to which a source of pressurized fluid P+ is connected. Left and right control ports 61 and 63, respectively, receive an alternating-flow input signal differentially thereacross. Left output passage 65 is connected to a capacitor 69 which in turn is connected to an inductor 71 while right output passage 67 is connected to capacitor 73 which in turn is connected to an inductor 75.

Inductor 71 in turn is connected to left control port 77 of second amplifier stage 55. Inductor 75 is connected to right control port 79 of amplifier 55. In addition, amplifier 55 has a power nozzle 81, left output passage 83, and right output passage 85. A source of pressurized fluid P+ is connected to power nozzle 81. Capacitors 87 and 89 are connected to output passages 83 and 85, respectively, and inductors 91 and 93 are connected to respective capacitors 87 and 89.

Amplifier 57 is the third and output stage of the circuit of FIG. 5 and includes a power nozzle 95, left and right control ports 97 and 99, respectively, and left and right output passages 101 and 103, respectively. A source of pressurized fluid P+ is connected to power nozzle 95. Left control port 97 is connected to inductor 91 in series relation and right control port 99 is connected to inductor 93 in series relation. The output passages 101 and 103 provide the amplified alternating flow output signal from the circuit of FIG. 5.

The frequency response characteristic of the circuit of FIG. 5 may take the general configuration illustrated in FIG. 2. The height and width of the resonant peak are dependent upon a number of considerations, among them the resonant frequencies to which the various L--C circuits are tuned. Suppose, for example, that all of the L-C circuits (capacitor 69 and inductor 71; capacitor 73 and inductor 75; capacitor 87 and inductor 91; capacitor 89 and inductor 93) are tuned to the same frequency. The resonant spike in the frequency response characteristic will then be quite narrow and the peak will be relatively high. On the other hand, spacing the tuned frequencies somewhat will tend to broaden the passband of the circuit and lower the level of the resonant gain somewhat.

Referring now to FIG. 6 of the accompanying drawings, there is illustrated a modulated-carrier fiuidic circuit employing a tuned fiuidic amplifier, provided in accordance with the principles of the present invention, for amplifying a directflow fluid signal. The direct-flow input signal is applied to a fiuidic amplitude-modulator 105 which also receives an oscillatory fluid carrier signal of constant amplitude and frequency. Amplitude-modulator 105 may, by way of example, be of the type disclosed in copending US. Pat. No. 3,428,067 referred to above, although any fluidic amplitude-modulator may be utilized for purposes of the circuit of FIG. 6. The output signal from amplitude-modulator 105 is an alternatingflow signal of constant frequency; namely, the frequency of the carrier signal, and has an amplitude envelope which varies in accordance with the amplitude of the direct-flow analog input signal applied to the amplitude modulator 105. The output signal from the amplitude-modulator is thus an alternating-flow signal which is applied to a tuned fluidic amplifier circuit 107, such asone or more stages of amplifiers employing either distributed parameter tuning as illustrated in FIG. 4 or lumped parameter tuning as illustrated in FIG. 5. Amplifier circuit 107 is tuned to the frequency of the oscillatory carrier signal applied to modulator 105. Since the signal applied to the tuned fluidic amplifier circuit 107 is of substantially constant frequency, it is preferable that a relatively narrow-band high-gain (high response be provided for the amplifier circuit, the band being centered on the carrier signal frequency. Techniques for minimizing resistive losses and thereby increasing circuit Q have been discussed above. The amplified amplitude-modulated signal is then applied to a filter 109, such as the low pass filter disclosed in U.S. Pat. No. 3,292,648, for the purpose of attenuating all harmonics of the resonant frequency of tuned fluidic amplifier circuit 107 above the fundamental frequency. In some applications, a harmonic of the fundamental resonant frequency of amplifier circuit 107 may be the desired operating frequency, in which case the carrier signal will be at the frequency of the specified harmonic and a bandpass filter will be employed to attenuate all frequency signals other than the specified harmonic. Where filtering is not desired filter 109 may be dispensed with. The output signal from filter 1 09 is applied to a demodulator 11 of the type disclosed in U.S. Pat. No. 3,292,648 and which serves to convert a signal applied thereto from alternating-flow to direct-flow and smoothes the converted signal to thereby provide an output signal corresponding to an amplified version of the direct-flow analog fluid input signal applied to amplitude modulator 105, the amplification being performed by tuned amplifier circuit 107.

' Amplifier circuit 107, of course, may comprise more than one amplifier stage depending upon the amount of gain desired. 1

Referring now to FIG. 7 of the accompanying drawing, there is illustrated an altemating-flow modulated-carrier fluidic system employing frequency modulation techniques. A direct-flow analog fluid input signal is applied to a frequencymodulator unit 113 which by way of example may be a pressure controlled oscillator of the type illustrated and described in U.S. Pat. No. 3,238,960 referred to above. The output signal from frequency-modulator 113 is an oscillatory fluid signal of constant amplitude and'having a frequency which varies as a direct function of the amplitude of the direct-flow analog fluid input signal applied thereto. The output signal from frequency-modulator 113 is therefore an alternatingflow signal which is applied to a tuned amplifier circuit 115 which, by way of example, may comprise one or more stages of tuned fluidic amplifiers using either lumped (FIG. or distributed parameter (FIG. 4) tuning techniques. Tuned circuit 115 preferably has a broader band frequency response than does circuit 107 of FIG. 6 because the frequency of the input signal applied to circuit 115 is variable whereas the signal applied to circuit 107 is of constant frequency. The pass-band of amplifier circuit 115 is preferably broad enough to encompass the entire operating range of frequency-modulator 113, the broadening of the frequency response of amplifier circuit 115 being accomplished by stagger-tuning techniques or varying the impedances in the resonant passages of the amplifier stages, orany of the other techniques discussed above in regard to the circuits of FIGS. 4 and 5. To compensate for the lower resonant gain which results from broadening the frequency response, additional amplifier stages may be used. The output signal provided by circuit 115 is applied to a filter 1 17 which, like filter 109 in FIG. 6, attenuates frequency components outside the range of interest. The output signal from filter 117 is applied to a demodulator unit 119, for example of the type described and illustrated in U.S. Pat. No. 3,292,648. Demodulator 119 like demodulator 111 in FIG. 6, serves to convert the alternating-flow signal to a direct flow signal and provide whatever signal smoothing effect is necessary to produce an amplified version of the direct flow analog signal applied to frequency-modulator 113.

While we have described and illustrated several embodiments of our i nvention,-it will be clear that variations of the details of construction which are specifically illustrated and described may be resorted to without departing from the true spirit and scope of the invention as defined in the-appended claims.

We claim:

1. A tuned fluidic flow amplifier circuit for amplifying input fiowfrequency components within a predetermined frequency range to a greater degree than input flow frequency components outside said predetermined frequency range, said circuit comprising:

a relatively low-impedance fluidic flow amplifier having a power nozzle of specified width and responsive to application of pressurized fluid thereto for issuing a power stream of fluid along a predetermined axis, at least one fluid receiver disposed downstream of said power nozzle for receiving power stream flow as a function of power stream direction and having an ingress orifice wider than said specified width, and control port means responsive to application of said input flow thereto for establishing a pressure gradient across said power stream to selectively vary the direction of said power stream relative to said ingress orifice of said fluid receiver, said control port means being arranged to substantially inhibit momentum interchange between said input flow and said power stream;

passive circuit means connected to said fluid receiver for providing an output flow in response to power stream flow into the ingress orificeof said fluid receiver, said passive circuit means having at least one resonant frequency f, lying in said predetermined'frequency range such that said output flow is substantially larger when power stream flow into said ingress orifice is at said resonant frequency than when at frequencies lying outside said predetermined frequency range, said passive fluidic circuit means comprising a fluid passage of substantially uniform cross section and predetermined length I such that f,=u/2l, where u is the speed of sound in the fluid of said fluid stream.

2. The combination according to claim 1 wherein said specified width of said power nozzle is W and the width of the ingress orifice of said receiver is approximately 3W.

3. The combination according to claim 1 wherein said control port means comprises a control port having an egress opening from which said input flow is directed toward said power stream, said egress opening being wider than said power nozzle and terminating at a distance from said predetermined axis which is approximately equal to said specified width.

4. The combination according to claim 3 wherein said specified width of said power nozzle is W, the width of the ingress orifice of said receiver is approximately 3W, and the width of said egress opening of said control port is approximately 3W.

5. The combination according to claim 4 further comprisa second fluid receiver having an ingress orifice with a width of approximately 3W disposed downstream of said power nozzle for receiving said power stream as a function of power stream direction;

further passive circuit means connected to said second fluid receiver for providing an output flow in response to power stream flow into the ingress orifice of said second fluid receiver, said further passive circuit having at least one resonant frequency lying in said predetermined frequency range such that said output flow from said further passive circuit means is substantially larger when power stream flow into the ingress orifice of said second fluid receiver is at the resonant frequency of said further passive fluidic circuit then when at frequencies lying outside said predetermined frequency range.

6. The combination according to claim 5 wherein said further passive circuit means comprises a further fluid passage means for providing an intelligence-bearing fluid input signal having a variable amplitude;

means for providing an oscillatory fluid signal of constant amplitude and at a frequency within said predetermined frequency range;

modulator means for amplitude-modulating said oscillatory fluid signal with said intelligence-bearing fluid signal to provide an amplitude-modulated fluid signal;

means for applying said amplitude-modulated signal to said control port of said fluidic amplifier as an input flow thereto; and

demodulator means connected to the downstream end of at least one of said resonant passages for detecting and smoothing the amplitude envelope of the output flow signal from said resonant passages to provide an amplified version of said intelligence-bearing fluid input signal substantially devoid of frequency components of said oscillatory fluid signal.

8. In a system employing the combination according to claim 6:

means for providing an intelligence-bearing fluid signal having a variable amplitude;

frequency-modulator means responsive to said intelligence- 7 bearing fluid signal for providing an oscillatory fluid signal of substantially constant amplitude and having a frequency which varies as a function of said variable amplitude and which lies in said predetermined frequency range;

means for applying said oscillatory fluid signal to said control port of said fluidic amplifier as an input flow thereto;

frequency-demodulator means connected to the downstream end of at least one of said resonant fluid passages for providing an output signal having an amplitude which is proportional to the frequency of the signal applied thereto, said output signal being an amplified version of said intelligence-bearing signal substantially devoid of frequency components of said oscillatory fluid signal.

9. The combination according to claim 1 wherein said fluidic amplifier is symmetrical about a centerline extending coaxial with said predetermined axis, said fluidic amplifier further comprising:

a second fluid receiver configured substantially identical to said first-mentioned fluid receiver and disposed on the opposite side of said centerline therefrom;

a second control port configured substantially identical to said first-mentioned control port and disposed on the opposite side of said power stream therefrom, said control ports being responsive .to application of fluid input thereto for establishing a pressure gradient across said power stream to selectively deflect said power stream in respective opposite senses relative to said centerline;

wherein said control ports are disposed in substantial opposition and are spaced from one another by approximately twice the specified width of said power nozzle.

10. The combination according to claim 9 wherein said control ports each have egress openings from which said control fluid is directed toward said power stream, the width of said egress openings being large relative to said specified width of said power nozzle.

1l. The combination according to claim 10 wherein the specified width'of said power nozzle is W, the width of the ingress orifices of said fluid receivers is approximately 3W, and the width of the egress openings of said control ports is approximately 3W.

12. The combination according to claim ll further comprising further passive circuit means connected to said second fluid receiver for providing an output flow in response to power stream flow into the ingress orifice of said second fluid receiver, said further passive circuit having at least one resonant frequency equal to said at least one resonant frequency of said first-mentioned passive fluidic circuit means such that said output flow from said further passive fluidic circuit means is substantially larger when power stream flow into the ingress orifice of said second fluid receiver is at said resonant frequency than when at frequencies lying outside saidpredetermined frequency range.

13. The combination according to claim 12 wherein said passive circuit means comprises a further fluid passage of said substantially uniform cross section and said predetermined length, said fluid passages being configured to produce standing waves therein in response to fluid flow disturbances at respective ingress orifices.

14. In a system employing the combinationaccording to claim 13:

means for providing an intelligence-bearing fluid signal having a variable amplitude;

modulator means for converting said intelligence bearing signal to an oscillatory fluid. signal having a parameter which varies as a function of the amplitude of said intelligence-bearing fluid signal, the frequency of said oscillatory signal being limited to said predetermined frequency range;

means for applying said oscillatory fluid signal to the control ports of said fluidic amplifier as an input flow thereto;

demodulator means connected to the downstream ends of said resonant fluid passages for detecting and smoothing the amplitude envelope of the output flows providedby said resonant fluid passages to provide an amplified version of said intelligence-bearing fluid signal substantially devoid of frequency components of said oscillatory fluid signal.

15. A tuned fluidic flow amplifier circuit for amplifying input flow frequency components within a predetermined frequency range to a greater degree than input flow frequency components outside said predetermined frequency range, said circuit comprising:

a relatively low-impedance fluidic flow amplifier having a power nozzle of specified width and responsive to application of pressurized fluid thereto for issuing a power stream of fluid along a predetermined axis, at least one fluid receiver disposed downstream of said power nozzle for receiving power stream flow as a function of power stream direction and having an ingress orifice wider than said specified width, and control port means responsive to application of said input flow thereto for establishing a pressure gradient across said power stream to selectively vary the direction of said power stream relative to said ingress orifice of said fluid receiver, said control port means being arranged to substantially inhibit momentum interchange between said input flow and said power stream; passive circuit means connected to said fluid receiver for providing an output flow in response to power stream flow into the ingress orifice of said fluid receiver, said passive circuit means having at least one resonant frequency lying in said predetermined frequency range such that said output flow is substantially larger when power stream flow into said ingress orifice is at said resonant frequency than when at frequencies lying outside said predetermined frequency range; V I wherein said control port extends substantially perpendicular to the direction of power stream flow, and wherein the egress opening of the control port is defined on its downstream side by a wall of knife-edge configuration having its apex directed generally toward the power stream, said wall terminating at a distance W from said predetermined axis. 16. The combination according to claim 15 wherein said passive circuit means includes a resonant fluid passage connected to said fluid receiver, said fluid receiver and said resonant fluid passage having the same constant cross section throughout their lengths, said fluid receiver and said resonant fluid passage being configured to produce standing waves therein in response to fluid inflow to said ingress orifice, said I standing waves being at a frequency determined by the combined length of said fluid receiver and said resonant fluid passage, said combined length being selected to provide said standing waves at said resonant frequency.

17. The combination according to claim 15 wherein the distance between said power nozzle and said ingress orifice is between eight and 15 times said specified width.

18. The combination according to claim 15 wherein said passive circuit means comprises a resonant fluid passage extending a predetermined length from the ingress orifice of said fluid receiver, said resonant fluid passage being configured to produce standing pressure waves therein in response to pressure disturbances at said ingress orifice, said standing waves having a frequency equal to said resonant frequency as determined by said predetermined length.

19. The combination according to claim 18 wherein said resonant fluid passage is of substantially uniform cross section throughout its length.

20. A tuned fluidic flow amplifier circuit for amplifying input flow frequency components within a predetermined frequency range to a greater degree than input flow frequency components outside said predetermined frequency range, said circuit comprising:

a relatively low-impedance fluidic flow amplifier having a power nozzle of specified width and responsive to application of pressurized fluid thereto for issuing a power stream of fluid along a predetermined axis, at least one fluid receiver disposed downstream of said power nozzle for receiving power stream flow as a function of power stream direction and having an ingress orifice wider than said specified width, and control port means responsive to application of said input flow thereto for establishing a pressure gradient across said power stream to selectively vary the direction of said power stream relative to said ingress orifice of said fluid receiver, said control port means being arranged to substantially inhibit momentum interchange between said input flow and said power stream;

passive circuit means connected to said fluid receiver for providing an output flow in response to power stream flow into the ingress orifice of said fluid receiver, said passive circuit means having at least one resonant frequency lying in said predetermined frequency range such that said output flow is substantially larger when power stream flow into said ingress orifice is at said resonant frequency than when at frequencies lying outside said predetermined frequency range;

wherein said control port means comprises a control port having an egress opening from which said input flow is directed toward said power stream, said egress opening being wider than said power nozzle and terminating at a distance from said predetermined axis which is approximately equal to said specified width;

wherein said specified width of said power nozzle is W, the

width of the ingress orifice of said receiver is approximately 3W, and the width of said egress opening of said control port is approximately 3W;

the combination further comprising:

a second fluid receiver having an ingress orifice with a width of approximately 3W disposed downstream of said power nozzle for receiving said power stream as a function of power stream direction;

further passive circuit means connected to said second fluid receiver for providing an output flow in response to power stream flow into the ingress orifice of said second fluid receiver, said further passive circuit having at least one resonant frequency lying in said predetermined frequency range such that said output flow from said further passive circuit means is substantially larger when power stream flow into the ingress orifice of said second fluid receiver is at the resonant frequency of said furtherpassive fluidic circuit than when at frequencies lying outside said predetermined frequency range;

wherein each of said passive fluidic circuit means comprises a lumped parameter fluid inductor-capacitor circuit connected in series with a respective one of said receivers, said inductor-capacitor circuit being tuned to said resonant frequency;

means for providing an intelligence-bearing fluid input signal having a variable amplitude;

means for providing an oscillatory fluid signal of constant amplitude and at a frequency within said predetermined frequency range;

modulator means for amplitude-modulating said oscillatory fluid signal with said intelligence-bearing fluid signal to provide an amplitude-modulated signal;

means for applying said amplitude modulated signal to said control port of said fluidic amplifier as an input flow thereto; and

demodulator means connected to said inductor-capacitor circuit for demodulating the output flow signal provided by said inductor-capacitor circuit to provide a signal which is an amplified version of said intelligence-bearing input signal.

21. A tuned fluidic flow amplifier circuit for amplifying input flow frequency components within a predetermined frequency range to a greater degree than input flow frequency components outside said predetermined frequency range, said circuit comprising:

a relatively low-impedance fluidic flow amplifier having a power nozzle of specified width and responsive to application of. pressurized fluid thereto for issuing a power stream of fluid along a predetermined axis, at least one fluid receiver disposed downstream of said power nozzle for receiving power streamflow as a function of power stream direction and having an ingress orifice wider than said specified width, and control port means responsive to application of said input flow thereto for establishing a pressure gradient across said power stream to selectively vary the direction of said power stream relative to said ingress orifice of said fluid receiver, said control port means being arranged to substantially inhibit momentum interchange between said input flow and said power stream;

passive circuit means connected to said fluid receiver for providing an output flow in response to power stream flow into the ingress orifice ofsaid fluid receiver, said passive circuit means having at least one resonant frequency lying in said predetermined frequency range such that said output flow is substantially larger when power stream flow into said ingress orifice is at said resonant frequency than when at frequencies lying outside said predetermined frequency range;

wherein said specified width of said power nozzle is W and the width of the ingress orifice of said receiver is approximately 3W;

wherein said control port means comprises a control port having an egress opening from which said input flow is directed toward said power stream, said egress opening being wider than said power nozzle and terminating at a distance from said predetermined axis which is approximately equal to said specified width;

and the width of said egress opening of said control port is approximately 3W;

the combination further comprising:

a second fluid receiver having an ingress orifice with a width of approximately 3W disposed downstream of said power nozzle for receiving said power stream as a function of power stream direction;

further passive circuit means connected to said second fluid receiver for providing an output flow in response to power stream flow into the ingress orifice of said second fluid receiver, said further passive circuit having at least one resonant frequency lying in said predetermined frequency range such that said output flow from said further passive circuit means is substantially larger when power stream flow into the ingress orifice of'said second fluid receiver is at the resonant frequency of said further passive fluidic circuit than when at frequencies lying outside said predetermined frequency range;

wherein each of said passive fluidic circuit means comprises a lumped parameter fluid inductor-capacitor circuit connected in series with a respective one of said receivers, said inductor-capacitor circuit being tuned to said resonant frequency;

means for providing an intelligence-bearing fluid signal having a variable amplitude of interest;

frequency-modulator means responsive to said intelligencebearing fluid signal for providing an oscillatory fluid signal of substantially constant amplitude and having a frequency which varies as a function of said variable amplitude and which lies in said predetermined frequency range;

means for applying said oscillatory fluid signal to said control port of said fluidic amplifier as an input flow thereto;

frequency-demodulator means connected to said inductorcapacitor circuit for demodulating the fluid flow output signal provided by said inductor-capacitor circuit to provide an output signal which is an amplified version of said intelligence-bearing signal.

22. A tuned fluidic flow amplifier circuit for amplifying input flow frequency components within a predetermined frequency rangeto a greater degreee than input flow frequency components outside said predetermined frequency range, said circuit comprising:

a relatively low-impedance fluidic flow amplifier having a power nozzle of specified width and responsive to application of pressurized fluid thereto for issuing a power stream of fluid along a predetermined axis, at least one fluid receiver disposed downstream of said power nozzle for receiving power stream flow as a function of power stream direction and having an ingress orifice wider than said specified width, and control port means responsive to application of said input flow thereto for establishing a pressure gradient across said power stream to selectively vary the direction of said power stream relative to said ingress orifice of said fluid receiver, said control port means being arranged to substantially inhibit momentum interchange between said input flow and said power stream;

passive circuit means connected to said fluid receiver for providing an output flow in response to power stream flow into the ingress orifice of said fluid receiver, said passive circuit means having at least one resonant frequency lying in said predetermined frequency range such that said output flow is substantially larger when power stream flow into said ingress orifice is at said resonant frequency than when at frequencies lying outside said predetermined frequency range;

means for providing an intelligence-bearing fluid signal having a variable amplitude;

modulator means for converting said intelligence-bearing fluid signal to an oscillatory fluid signal having a frequency which is limited to said predetermined frequency range and having a parameter which varies as a function of said variable amplitude of said intelligence-bearing fluid signal;

means for applying said oscillatory fluid signal to the control port of said fluidic amplifier as an input flow thereto;

demodulator means responsive to said output fluid flow signal from said passive fluidic circuit means for providing an amplified version of said intelligence-bearing fluid signal substantially devoid of frequency components of said oscillatory fluid signal. I

23. A tuned fluidic amplifier circuit for amplifying input flow frequency components within a predetermined frequency range to a greater degree than input flow frequency components outside said predetermined frequency range, said circuit comprising:

a plurality of low-impedance fluidic amplifiers of the type which respond to input flow applied thereto by providing amplified output flow;

interstage tuning means for connecting said plurality of lowimpedance fluidic amplifiers in cascade relation, said interstage tuning means each comprising passive resonant means having a resonant frequency within said predetermined frequency range for reinforcing flow frequency components applied to said interstage tuning means at said resonant frequencyand impeding flow frequency components applied to said interstage tuning means at frequencies outside said predetermined frequency range;

wherein said plurality of cascaded amplifiers number at least three, and wherein said passive resonant fluidic means interconnecting the first and second amplifier stages has a resonant frequency slightly different from the resonant frequency of said passive resonant fluidic means interconnecting said second and third amplifier stages, whereby to provide a stagger-tuned amplifier circuit.

24. A tuned fluidic amplifier circuit for amplifying frequency components of fluid flo'w signals within a predetermined frequency range to a greater degree than frequency components outside said predetermined frequency range, said circ-uit comprising: I

a fluidic flow amplifier including: an interaction region having upstream and downstream ends; a power nozzle of specified width having a longitudinal axis and responsive to application of pressurized fluid thereto for issuing a power stream of fluid along said longitudinal axis and into said interaction region from said upstream end toward said downstream end; at least one fluid receiver having an ingress orifice of width greater than said specified width and disposed at said downstream end of said interaction region in receiving relation to said power stream; at least one control passage communicating with said interaction region at one side thereof approximate said upstream end and arranged to issue fluid applied thereto and generally toward said power stream, said control passage having upstream and downstream sidewalls separated by more than said specified width, said downstream sidewall terminating downstream of said power nozzle at a distance from said longitudinal axis approximately equal to said specified width; and a vent passage communicating between ambient pressure environment and a location in said interaction region between said control channel and said power nozzle;

passive circuit means connected to said fluid receiver for providing an output flow signal in response to fluid flow into said ingress orifice of said fluid receiver, said passive circuit means comprising a resonant fluid passage extending from said fluid receiver a predetermined length from said ingress orifice, said resonant fluid passage being of substantially uniform cross section throughout its length and being configured to produce standing pressure waves therein in response to disturbances occurring at said ingress orifice, said standing waves being at a resonant frequency lying in said predetermined frequency range such that fluid flow into said ingress orifice of said fluid receiver is amplified when at said resonant frequency and is substantially attenuated when at frequencies lying outside said predetermined frequency range. 

